This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on patent application No. 2001-151070 filed in Japan on May 21, 2001, the entirety of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel injection control system for an engine, and more particularly to a fuel injection control system for an engine capable of estimating a portion of a fuel injected from a fuel injection valve that is not directly supplied to a cylinder because of adhesion along an inner wall of an intake pipe or the like. Accordingly, adequate fuel injection on the basis of this estimated result is realized with the present invention.
2. Description of the Background Art
Control systems for engines in which fuel injection valves are disposed in the upstream and the downstream of a throttle valve have been known in the background art. For example, a similar control system is described in Japanese Patent Laid-open No. Hei 6-102999. This control system is configured such that a fuel is injected, in an idle rotation region, only from a downstream side fuel injection valve. Fuel is injected, in a region other than the idle rotation region, from an upstream side fuel injection valve in accordance with an engine operation state.
In this type of control unit, when the control unit operates in a region other than the idle rotation region, a fuel amount injected from the downstream side injection valve is gradually reduced to a target value. The fuel amount injected from the downstream side injector is determined in consideration of the residual portion of a fuel injected from the upstream side injection valve. The residual portion adheres on a wall surface of an intake pipe.
Fuel injection control systems for engines having a single fuel injection valve, in which a fuel injection amount is corrected in consideration of fuel adhering on an inner wall of an intake pipe, have been proposed in the background art. For example, in Japanese Patent Laid-open Nos. Hei 7-247892 and Hei 5-340285 single fuel injection valve systems are described. In particular, the control system in the latter document discloses controlling repeated fuel injection (divided injection), i.e., twice in one cycle.
According to the control system described in Japanese Patent Laid-open No. Hei 6-102999, although adhesion of a fuel on the wall surface in the upstream of the throttle valve is taken into account, it fails to examine an amount of the fuel adhering on the wall surface along the lower and remaining surfaces. Accordingly, the control system does not realize high, accurate control so as to meet a target air-fuel ratio. It is therefore difficult to improve drivability (running performance) in combination with the desired improvement of fuel consumption. Another problem of this control system is that since the number of setting parameters is increased to improve responsiveness to a change in engine state, or a change in throttle opening angle, the control of fuel injection becomes complex.
The fuel injection control system for an engine including a single fuel injection valve estimates a fuel adhesion amount specified for an engine including a single fuel injection valve. The control system does not control fuel individually in an engine including fuel injection valves disposed in the upstream and downstream of the throttle valve. Accordingly, the control systems of the background art do not estimate a fuel adhesion amount in each of the upstream and downstream positions with respect to the throttle valve in an engine including fuel injection valves disposed in both the upstream and downstream positions.
As described in the above document, Japanese Patent Laid-open No. Hei 6-102999, the calculation of a fuel injection amount is generally performed at each predetermined crank angle (at each crank angle of 180xc2x0 in the control system of this document). Fuel is injected front each fuel injection valve at a rate of once per cycle (crank angle: 720xc2x0).
Accordingly, if an engine state is changed before a point of fuel injection and after calculation of a fuel injection amount is calculated, the fuel injection amount once determined cannot be changed. As a result, in an acceleration state in which the engine state is changed rapidly and/or significantly, the amount of fuel supplied may be lacking to the point of degrading drivability and/or engine operability. In particular, if a throttle opening angle is changed significantly, it is unclear to what degree a fuel injected from an upstream injection valve flows in the downstream of the throttle valve, with a result that over-rich or over-lean engine operation is liable to occur. The entirety of each of the foregoing references described in the Description of the Background Art of the present application are hereby incorporated by reference into the present application.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
An object of the present invention is to provide a fuel injection control system for an engine capable of accurately determining an amount of fuel supplied in response to a current engine state on the basis of a fuel flow-in state from a position upstream of a throttle valve.
These and other aspects of the present invention are accomplished by a fuel injection control system for an engine comprising a throttle valve; at least one upstream injection valve being,disposed in an upstream position with respect to the throttle valve; at least one downstream injection valve being disposed in a downstream position with respect to the throttle valve; means for calculating a required fuel amount for a predetermined calculation cycle and calculating actual fuel amounts to be injected during a fuel injection process from the upstream injection valve and the downstream injection valve on the basis of the required fuel amount; and means for calculating, after the fuel injection process, a lack of fuel amount immediately before recalculating a recalculated required fuel amount at the calculation cycle coming at the end of an intake stroke, the lack of fuel amount being calculated by subtracting the required and the actual fuel amounts from the recalculated required fuel amount.
These and other aspects of the present invention are further accomplished by a method of calculating a fuel injection amount for a cylinder using the foregoing system, the method comprising calculating a fuel injection amount of at least one of the upstream fuel injection valve and the downstream fuel injection valve according to a respective fuel pressure of the upstream fuel injection valve and the downstream fuel injection valve; and controlling a fuel injection time period to control the fuel injection amount.
These and other aspects of the present invention are further accomplished by a fuel injection control system for an engine including a fuel injection valve, the fuel injection control system comprising means for calculating a required fuel amount during a predetermined calculation cycle and for calculating a injected fuel amount to be injected from the fuel injection valve on the basis of the required fuel amount; means for calculating, after a fuel injection of a fuel from the fuel injection valve on the basis of the calculated injected fuel amount, a lack of fuel amount immediately before a re-calculation of a required fuel amount during the calculation cycle at the end of an intake stroke, the lack of fuel amount being calculated by subtracting the calculated injected fuel amount from the re-calculated required fuel amount; the lack of fuel amount being additionally injected during the intake stroke; the lack of fuel injection amount being calculated by addition of a fuel injected from the fuel injection valve and deposited on an inner wall of an intake pipe to achieve a first amount, and subtracting a fuel released from the deposited fuel to flow into an engine cylinder from the first amount.
These and other aspects of the present invention are further accomplished by a fuel injection control system for an engine comprising at least one engine cylinder; a throttle valve; at least one upstream injection valve being disposed in an upstream position with respect to the throttle valve; at least one downstream injection valve being disposed in a downstream position with respect to the throttle valve; a direct fuel flow calculating unit; an indirect fuel flow calculating unit; a downstream fuel calculating unit, the downstream fuel calculating unit outputting a combined fuel flow from the upstream position and the downstream injection valve; a downstream direct fuel flow calculating unit; a downstream indirect fuel flow calculating unit; an adding unit, the adding unit outputting an actual fuel amount to the cylinder; and a comparison unit, the comparison unit calculating a lack of fuel amount immediately before recalculating a recalculated required fuel amount at a calculation cycle coming at the end of an intake stroke of the cylinder, the lack of fuel amount being calculated by subtracting a sum of a required fuel amount and the actual fuel amount from the recalculated required fuel amount.
These and other aspects of the present invention are further accomplished by a method of calculating a fuel injection amount for a cylinder using the foregoing system, the method comprising calculating a fuel injection amount of at least one of the upstream fuel injection valve and the downstream fuel injection valve; and controlling a fuel injection time period to control the fuel injection amount.
With a first feature of the present invention, after a fuel based on a required fuel amount calculated at a predetermined cycle is injected, any fuel deficit from the previous fuel injection can be calculated and additionally injected up until the end of the intake stroke.
With second and third features of the present invention, the lack of fuel injection amounts can be accurately detected by estimating the amount of a fuel supplied not directly, but indirectly from each fuel injection valve to the engine in accordance with the predetermined adhesion ratio and the predetermined release ratio.
With a fourth feature of the present invention, the lack of fuel injection amount can be accurately detected by calculating a portion of a fuel injected from the fuel injection valve. This portion directly flows into the cylinder. A second portion of the fuel injected from the fuel injection valve, which part has been deposited on the inner wall of the intake pipe, and is subsequently released to indirectly flow into the cylinder, makes up the additional fuel that can be supplied to the engine with the first portion, e.g. a total fuel amount.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.